Mercurial > sdl-ios-xcode

annotate src/thread/dc/SDL_syscond.c @ 4347:38f22ed3a433 SDL-1.2

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Option to fix bug #851 For some people setting the period size works better (and is what SDL 1.2.13 did), but for most people it's the same or worse. You can use an environment variable to pick which one you want.
author Sam Lantinga <slouken@libsdl.org>
date Sat, 17 Oct 2009 06:55:17 +0000
parents a1b03ba2fcd0
children
rev   line source
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1 /*
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2 SDL - Simple DirectMedia Layer
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3 Copyright (C) 1997-2009 Sam Lantinga
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4
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5 This library is free software; you can redistribute it and/or
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6 modify it under the terms of the GNU Lesser General Public
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7 License as published by the Free Software Foundation; either
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8 version 2.1 of the License, or (at your option) any later version.
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9
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10 This library is distributed in the hope that it will be useful,
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11 but WITHOUT ANY WARRANTY; without even the implied warranty of
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12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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13 Lesser General Public License for more details.
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14
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15 You should have received a copy of the GNU Lesser General Public
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16 License along with this library; if not, write to the Free Software
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17 Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
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18
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19 Sam Lantinga
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20 slouken@libsdl.org
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21 */
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22 #include "SDL_config.h"
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23
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24 /* An implementation of condition variables using semaphores and mutexes */
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25 /*
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26 This implementation borrows heavily from the BeOS condition variable
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27 implementation, written by Christopher Tate and Owen Smith. Thanks!
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28 */
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29
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30 #include "SDL_thread.h"
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31
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32 struct SDL_cond
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33 {
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34 SDL_mutex *lock;
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35 int waiting;
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36 int signals;
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37 SDL_sem *wait_sem;
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38 SDL_sem *wait_done;
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39 };
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40
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41 /* Create a condition variable */
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42 SDL_cond * SDL_CreateCond(void)
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43 {
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44 SDL_cond *cond;
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45
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46 cond = (SDL_cond *) SDL_malloc(sizeof(SDL_cond));
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47 if ( cond ) {
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48 cond->lock = SDL_CreateMutex();
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49 cond->wait_sem = SDL_CreateSemaphore(0);
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50 cond->wait_done = SDL_CreateSemaphore(0);
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51 cond->waiting = cond->signals = 0;
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52 if ( ! cond->lock || ! cond->wait_sem || ! cond->wait_done ) {
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53 SDL_DestroyCond(cond);
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54 cond = NULL;
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55 }
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56 } else {
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57 SDL_OutOfMemory();
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58 }
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59 return(cond);
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60 }
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61
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62 /* Destroy a condition variable */
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63 void SDL_DestroyCond(SDL_cond *cond)
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64 {
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65 if ( cond ) {
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66 if ( cond->wait_sem ) {
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67 SDL_DestroySemaphore(cond->wait_sem);
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68 }
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69 if ( cond->wait_done ) {
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70 SDL_DestroySemaphore(cond->wait_done);
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71 }
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72 if ( cond->lock ) {
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73 SDL_DestroyMutex(cond->lock);
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74 }
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75 SDL_free(cond);
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76 }
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77 }
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78
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79 /* Restart one of the threads that are waiting on the condition variable */
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80 int SDL_CondSignal(SDL_cond *cond)
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81 {
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82 if ( ! cond ) {
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83 SDL_SetError("Passed a NULL condition variable");
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84 return -1;
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85 }
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86
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87 /* If there are waiting threads not already signalled, then
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88 signal the condition and wait for the thread to respond.
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89 */
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90 SDL_LockMutex(cond->lock);
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91 if ( cond->waiting > cond->signals ) {
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92 ++cond->signals;
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93 SDL_SemPost(cond->wait_sem);
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94 SDL_UnlockMutex(cond->lock);
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95 SDL_SemWait(cond->wait_done);
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96 } else {
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97 SDL_UnlockMutex(cond->lock);
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98 }
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99
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100 return 0;
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101 }
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102
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103 /* Restart all threads that are waiting on the condition variable */
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104 int SDL_CondBroadcast(SDL_cond *cond)
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105 {
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106 if ( ! cond ) {
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107 SDL_SetError("Passed a NULL condition variable");
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108 return -1;
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109 }
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110
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111 /* If there are waiting threads not already signalled, then
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112 signal the condition and wait for the thread to respond.
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113 */
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114 SDL_LockMutex(cond->lock);
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115 if ( cond->waiting > cond->signals ) {
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116 int i, num_waiting;
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117
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118 num_waiting = (cond->waiting - cond->signals);
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119 cond->signals = cond->waiting;
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120 for ( i=0; i<num_waiting; ++i ) {
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121 SDL_SemPost(cond->wait_sem);
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122 }
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123 /* Now all released threads are blocked here, waiting for us.
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124 Collect them all (and win fabulous prizes!) :-)
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125 */
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126 SDL_UnlockMutex(cond->lock);
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127 for ( i=0; i<num_waiting; ++i ) {
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128 SDL_SemWait(cond->wait_done);
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129 }
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130 } else {
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131 SDL_UnlockMutex(cond->lock);
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132 }
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133
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134 return 0;
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135 }
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136
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137 /* Wait on the condition variable for at most 'ms' milliseconds.
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138 The mutex must be locked before entering this function!
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139 The mutex is unlocked during the wait, and locked again after the wait.
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140
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141 Typical use:
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142
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143 Thread A:
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144 SDL_LockMutex(lock);
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145 while ( ! condition ) {
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146 SDL_CondWait(cond);
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147 }
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148 SDL_UnlockMutex(lock);
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149
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150 Thread B:
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151 SDL_LockMutex(lock);
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152 ...
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153 condition = true;
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154 ...
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155 SDL_UnlockMutex(lock);
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156 */
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157 int SDL_CondWaitTimeout(SDL_cond *cond, SDL_mutex *mutex, Uint32 ms)
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158 {
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159 int retval;
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160
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161 if ( ! cond ) {
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162 SDL_SetError("Passed a NULL condition variable");
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163 return -1;
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164 }
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165
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166 /* Obtain the protection mutex, and increment the number of waiters.
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167 This allows the signal mechanism to only perform a signal if there
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168 are waiting threads.
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169 */
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170 SDL_LockMutex(cond->lock);
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171 ++cond->waiting;
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172 SDL_UnlockMutex(cond->lock);
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173
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174 /* Unlock the mutex, as is required by condition variable semantics */
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175 SDL_UnlockMutex(mutex);
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176
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177 /* Wait for a signal */
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178 if ( ms == SDL_MUTEX_MAXWAIT ) {
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179 retval = SDL_SemWait(cond->wait_sem);
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180 } else {
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181 retval = SDL_SemWaitTimeout(cond->wait_sem, ms);
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182 }
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183
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184 /* Let the signaler know we have completed the wait, otherwise
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185 the signaler can race ahead and get the condition semaphore
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186 if we are stopped between the mutex unlock and semaphore wait,
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187 giving a deadlock. See the following URL for details:
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188 http://www-classic.be.com/aboutbe/benewsletter/volume_III/Issue40.html
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189 */
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190 SDL_LockMutex(cond->lock);
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191 if ( cond->signals > 0 ) {
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192 /* If we timed out, we need to eat a condition signal */
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193 if ( retval > 0 ) {
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194 SDL_SemWait(cond->wait_sem);
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195 }
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196 /* We always notify the signal thread that we are done */
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197 SDL_SemPost(cond->wait_done);
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198
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199 /* Signal handshake complete */
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200 --cond->signals;
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201 }
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202 --cond->waiting;
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203 SDL_UnlockMutex(cond->lock);
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204
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205 /* Lock the mutex, as is required by condition variable semantics */
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206 SDL_LockMutex(mutex);
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207
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208 return retval;
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209 }
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210
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211 /* Wait on the condition variable forever */
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212 int SDL_CondWait(SDL_cond *cond, SDL_mutex *mutex)
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213 {
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214 return SDL_CondWaitTimeout(cond, mutex, SDL_MUTEX_MAXWAIT);
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215 }